1. Field of the Invention
The invention herein relates to composition and structures for artificial human nails. More particularly, it relates to such compositions formed of polymeric materials.
2. Description of the Prior Art
Artificial finger nails (and toe nails) are major items of personal fashion. Artificial nails are normally formed by coating (as by applying with a brush) a viscous liquid layer of polymerizable material on the surface of the natural nail, shaping (as with a brush) and then allowing the coating material to polymerize and harden. In many cases polymerization can be speeded up by use of a catalyst or accelerator incorporated into the coating. Once polymerized and hardened, the artificial nail can be shaped and polished to present an attractive and natural appearance.
There are several basic types of artificial nail materials. One type exhibits a significant amount of vapor evolution during curing. The vapors frequently have a noticeable odor. While that odor quickly dissipates for the wearer, it persists in nail shops and the technicians who apply the nail surfaces to the customers are subjected to extended exposure to the vapors. In addition, this type of product shows limited strength and can have a pronounced tendency to discolor, crystallize and lift from the nail plate. The common monomeric compounds which are frequently used as polymerizable components of this type of nail surface are ethyl methacrylate (EMA) and isobutyl methacrylate.
A different type of nail materials are called "odorless materials," since they produce little or no vapor during polymerization. This type of material, however, has had its own disadvantages. They often form "skins" (i.e., unpolymerized surface layers) which must be removed. They form relatively thick coatings and cannot be readily picked up and coated by the nail technician's brush. In addition, they have a definite tendency to yellow and become brittle with age. Their use also requires a significant change in the conventional application techniques used by nail technicians, a change which many technicians dislike and resist. A common component used in this type of materials is hydroxyethyl methacrylate (HEMA).
Speed of polymerization (hardening or curing) is an important factor in the success of artificial nail products. Acceleration of reaction can usually be obtained only by using excess catalyst or accelerator or by heating. Heating, however, is impractical for artificial nail surfaces simply because the technician cannot apply significant heat to a customer's hands. Use of excess catalyst or accelerator is also undesirable because it usually makes the nail composition unacceptably brittle, such that the finished nail will break easily, and discolored. In the past, the prior art has attempted to overcome the problem of brittleness by adding rubber compounds to strengthen the nail, but the resulting phase separation caused by the rubber makes the composition opaque or translucent rather than having the desired transparency.
Another very significant problem in the application of artificial nail compositions, particularly in the nail systems utilizing EMA, has been "catastrophic crystallization." This occurs when the artificial nail composition, prior to becoming fully polymerized and hardened, comes in contact with cool air or air drafts. This results in the formation of crystal-like regions throughout the entire depth of the coating. Polymerization of the coating thereafter does not occur in these regions so that the overall artificial nail structure does not form properly. In such cases, the nail technician must remove the entire coating and start over with a completely new coating application. The additional length of time needed to completely redo a catastrophically crystallized nail coating is objected to by both the technicians and the customers as a time-consuming task for the technician and a major inconvenience for the customer.